M. TECHNOLOGY. 491 



recommends it strongly to travelers, and it has been stated 

 that Dr. Stein's invention will be adopted by the German 

 observers of the transit of Venus. Astron. Nachrichten, 

 LXXXIIL, 65. 



VANADATE OF AMMONIA FOR THE MANUFACTURE OF INK. 



The invariable detection, by Bottger, of vanadium in all 

 specimens of pisolitic limonite (Bohnerze), and the separating 

 it, by his process, in larger quantities than had been obtained 

 before, led him to call attention to the applicability of the 

 neutral vanadate of ammonia in the manufacture of a most 

 excellent, deep-black, very fluid writing-ink. This may be 

 made by triturating three parts of the salt with one part of 

 pyrogallic acid and three parts of finely pulverized gum ara- 

 ble in a porcelain mortar, with the addition of a suitable 

 amount of cold rain-water. The separation of the vanadium 

 from the iron ore is accomplished by pulverizing it very fine- 

 ly, mixing it with nitrate of potash and caustic soda, and 

 subjecting it to a red heat for a short time in a Hessian cru- 

 cible ; then extracting the mass with boiling water, and care- 

 fully adding to the filtered liquid so much nitric acid, free 

 from hyponitric acid, that but a slight alkaline reaction may 

 be retained. Solution of nitrate of baryta is then added to 

 the liquid filtered from the larger part of the silica and alu- 

 mina of the ore separated in this way, and from the insoluble 

 vanadate of baryta, thus formed, vanadic acid and other van- 

 adates are easily prepared. 15 C, 1873, xviii., 287. 



INCREASING THE SENSITIVENESS TO LIGHT OF BROMIDE OF 



SILVER. 



The insensibility of bromide of silver to certain colors of 

 the spectrum has been well established in practice, as also 

 its peculiar sensibility to invisible ultra-violet rays. Vogel 

 has shown that the sensibility of this preparation maybe car- 

 ried far into the red end of the spectrum, to regions where 

 hitherto photography has been impossible. His attention 

 seems first to have been called to this subject by receiving 

 some dry sensitive plates from England, which proved to be 

 more sensitive to the green than to the blue rays; and, in 

 general, he found that the dry bromide exhibited a more ex- 

 tended sensibility for colors than did the so-called wet plate. 



